Field of the Invention
The invention is directed to an improved acoustical fiberboard and the coating therefor. Methods for obtaining high noise reduction coefficients (NRC) are well known. NRC values are secured by using ASTM test C423-90a to measure the NRC of a product. Fiberglass is known to be a good sound absorber since it has high porosity. It can be decorated with a surface layer of laminated fabrics or painted scrims requiring only a minimal openness in the surface layer for sound to pass through and be absorbed in the substrate.
To make an acoustically high NRC (=or&gt;65) product using a wood or mineral fiberboard substrate, the board porosity must be high. Finish paint applied directly to the board also must not form a continuous film closing off the board surface. Normally this occurs thus lowering the NRC. A method generally used to increase the NRC is hole punching and surface perforations.
The desired product herein is to have a high NRC with a plain, nonperforated surface visual. If a sanded and painted fiberboard without surface perforations and scrim is the construction, then the porosity of the paint layer must be equal or greater than the porosity of the board in order to retain the sound absorption properties of the board. The special paint that enables high application rates providing adequate coverage while remaining porous is the subject of this invention. Attaining a high porosity and NRC=or&gt;65 is not easily accomplished with fiberboard without sacrificing other material properties such as strength and hardness.
If hole punching the fiberboard is needed to achieve the NRC=or&gt;65, then a facing layer is necessary in order to make a plain, nonperforated surface visual. Porous nonwoven scrims are attached for this purpose. Again a special paint is necessary to cover the scrim to make it optically opaque. Opacity is needed to hide the holes yet it must be acoustically transparent. The combination of the scrim and special paint herein is also the subject of this invention.